1. Field of the Invention
The present invention relates to an image projection apparatus (e.g., a projector) for projecting an image to a screen.
2. Description of Related Art
Recently, various types of projectors have become widespread. One of them is a projector PD′ disclosed in U.S. Pat. No. 6,805,447 B2 (hereinafter referred to as a patent document 1). This projector PD′, as shown in FIG. 7, uses a projection optical system PS′ that has a compact size and is capable of wide angle projection of image light to the rear surface of a screen SCN′. Such a projector PD′ is called a rear projector PD′ and is popular to users because it can save a space even in a small room.
In addition, the projector PD′ of the patent document 1 has a plane mirror MF′ disposed at a vicinity of the upper end of the screen SCN′ for leading image light from the projection optical system PS′. Therefore, the projection optical system PS′ can be disposed behind the screen SCN′. As a result, the height of the projector PD′ can be controlled. In other words, the projector PD′ is a projector PD′ having a short depth and a low height.
However, the projector PD′ of the patent document 1 has a disadvantage that part of image light to enter the plane mirror MF′ via the projection optical system PS′ may deviate from its optical path and may enter directly to the screen SCN′. Such part of image light is indicated by an arrow G1′ in FIG. 7, for example. If this image light G1′ enter the screen SCN′, image quality of the projector PD′ is deteriorated, which is undesired result.
Furthermore, if a space between the projection optical system PS′ and the screen SCN′ is reduced for realizing thinner projector PD′ of the patent document 1, the image light that enters the screen SCN′ from the plane mirror MF′ may deviate from a normal optical path and may enter a member for holding the projection optical system PS′ (a holder member, not shown), and further may be reflected after that. In this case, part of the reflected image light is indicated by an arrow G2′ in FIG. 7, for example. If this image light G2′ also enters the screen SCN′, image quality of the projector PD′ is deteriorated, which is undesired result.